This invention relates to a method for the preparation of emulsions of oil in water and more particularly the preparation of high internal phase ratio (HIPR) emulsions of viscous oils in water.
Many crude oils are viscous when produced and are thus difficult, it not impossible, to transport by normal methods from their production location to a refinery.
Several methods have been suggested for the transportation of such crudes by pipeline. These include (1) heating the crude and insulating the pipeline, (2) adding a non-recoverable solvent, (3) adding a recoverable solvent, (4) adding a lighter crude oil, (5) forming an annulus of water around the crude and (6) emulsifying the crude in water.
Methods (1)-(4) can be expensive in terms of added components and capital expenditure and method (5) is technically difficult to achieve.
Method (6) whilst superficially attractive presents special difficulties. The dispersion of a highly viscous oil in a medium of much lower viscosity is an unfavorable process on hydrodynamic grounds. This problem is further complicated by the economic requirement to transport emulsions containing relatively high oil phase volumes without sacrificing emulsion fluidity. Mechanical dispersing can lead to the formation of polydisperse or multiple emulsions, both of which are less suitable for transportation.
In the case of a system comprising dispersed spheres of equal size, the maximum internal phase volume occupied by a hexagonally close-packed arrangement is ca 74%. In practice, however, emulsions are rarely monodisperse and it is therefore possible to increase the packing density without causing appreciable droplet distortion. Attempts to increase further the internal phase volume results in greater droplet deformation and, because of the larger interfacial area created, instability arises; this culminates in either phase inversion or emulsion breaking. Under exceptional circumstances, it is possible to create dispersions containing as high as 98% disperse phase volume without inversion or breaking.
Emulsified systems containing 70% internal phase are known as HIPR emulsions. HIPR oil-in-water emulsions are normally prepared by dispersing increased amounts of oil into the continuous phase until the internal phase volume exceeds 70%. Clearly, for very high internal phase volumes, the systems cannot contain discrete spherical oil droplets; rather, they will consist of highly distorted oil droplets, separated by thin interfacial aqueous films.
A useful state-of-the-art review of HIPR emulsion technology is given in Canadian Patent No. 1,132,908.
British Patent Specification No. 1,283,462 discloses a method for producing an oil-in-water emulsion comprising beating up a mixture of the oil and water together with emulsifying agent in a vessel having a bottom exit to disperse the oil in droplets of an average size of not more than 10 microns in diameter throughout the water to form a concentrated emulsion, continuously withdrawing concentrated emulsion from the bottom exit of the vessel while simultaneously introducing components of the mixture into the top of the vessel to form further concentrated emulsion.
The oils are synthetic polymers or thickened animal or vegetable oils.
The action of the beater results in particle sizes in the dispersed phase of not more than 10 microns in diameter, usually from about 0.5 to 2 microns in diameter. The concentration of surfactant used is relatively high, 4-10% by weight of the total composition.
This results in concentrated, thick, extremely stable emulsions which have thixotropic properties and are useful as vehicles for paints or other coatings.
While U.S. Pat. No. 1,283,462 discloses that the concentrated emulsions are discharged through a short conduit from the emulsifying vessel to a tank in which they are further diluted, the concentrated emulsions are not suitable, nor are they intended, for transportation over long distances through relatively large diameter pipelines such as those used for the transportation of crude oil.
Furthermore, because of their extreme stability these emulsions cannot be, and are not intended to be, readily broken. Thus, they are unsuitable for applications where it is desired eventually to resolve the emulsions into their constituent parts, such as the treatment of crude oil where water must be removed before fractionation in an oil refinery distillation unit.